The present invention generally relates to a diode unit, and more particularly, to a semi-conductor laser unit such as an injection type semi-conductor laser unit (of a laser diode) and the like.
Recently, in the field of semi-conductor laser units, there has been a tendency that an injection type semi-conductor laser unit or a so-called laser diode is mainly employed, which is so arranged that a laser chip subjected to the PN junction, or single hetero-junction or a double hetero-junction is bonded on a substrate through a sub-mount, so that a laser may be emitted towards the outside from a front cleavage face of said laser chip.
Such semi-conductor laser units may be broadly divided into a so-called can seal type in which a window of a light-transmitting material capable of emitting outside the laser beam from the front cleavage face of a laser chip is provided on a can package for covering the unit, while the laser beam from a rear cleavage face of the laser chip is arranged to be received by a light receiving element of a photo-diode, and into an open unit type in which the laser chip subjected to the PN junction, or single hetero-junction or double hetero-junction is bonded on a substrate through a sub-mount. A while a light receiving element of a photo-diode is formed at a portion of the substrate for monitoring the laser beam from the rear cleavage face of the laser chip by the light receiving element.
In the semi-conductor laser unit of the open type referred to above, because the junction between the laser chip and the sub-mount, etc., is exposed to atmosphere, water component tends to enter the junction due to dew formation by the moisture to give rise to deterioration in the characteristics of the semi-conductor chip, thus resulting in inferior resistance against environmental conditions.